The present invention relates to a microcomputer controlled image processor which enables a laser transmitter to transmit optically phased laser beams from an array of multiple optical laser telescopes by calculating an optical path difference between pairs of laser beams which allows the laser transmitter to phase match transmitted laser beams.
Recent demands in telescope design for large primary telescopes have brought new emphasis to synthetic aperture applications. The idea of a synthetic aperture or phased array is not new and has been successfully applied in radar systems and astronomical telescopes. The new emphasis, though, is attempting to phase telescopes at visible wavelengths.
The successful application of phasing an array of multiple telescopes into a synthetic aperture extends the numerous benefits of using arrays, as experienced by radar systems, to optical laser telescopes. Phased arrays are modular. They can be built in stages and to some extent be operational as soon as the first telescope is operational. An array of independent telescopes has functional flexibility. Several simultaneous operations can be carried out by individual telescopes within a synthetic aperture. For example, images can be directed to different cameras or spectrographic devices for simultaneous observations in separate imaging modes. When operated as a transmitter, a synthetic aperture has the option of sending beams in different directions.
Phased array apertures have virtually no size limitations. By modularly combining telescopes in a phased configuration, laser transmitters of previously unimaginable sizes can be constructed. Large optics fabrication has historically posed an impermeable barrier to building large aperture telescope systems. By phasing a number of reasonably-sized telescopes, extremely large transmitting apertures can be achieved with present fabrication technology.
The present application hereby incorporates by reference the patent filed by Janet S. Fender et al, entitled "Optically Phased Laser Transmitter", in Air Force Invention No. 16,653, and U.S. Pat. No. 4,639,586.
The apparatus of the Fender patent is a laser transmitter which optically phases the output of an array of multiple optical laser telescopes to achieve the performance of a single laser transmitter of equivalent size.
The Fender apparatus performs matching between pairs of laser beams using an array containing at least two optical telescopes which become useable as a laser transmitter when combined with an optical phase matching system consisting of: a collecting telescope, a detector array, two fold mirrors, analog-to-digital converter, microprocessor, and two sets of correcting mirrors.
The two optical telescopes are adjacent to each other, and transmit two separate outgoing laser beams which require phase matching. The original source of the two outgoing beams may be either: a single laser beam, which has been divided (monochromatic); or two separately transmitted polychromatic laser beams.
The collecting telescope sits in front of the two optic telescopes and bridges the gap between them. In this way, the collecting telescope is able to intercept samples of outgoing laser beams from the edges of both telescopes and focus them, through the two fold mirrors to the detector array.
The detector array may be either a line scan or an area charge coupled device (CDD), which reads out the fringe pattern by generating an interference pattern.
The microcomputer controlled image processor of the present invention performs the functions attributed to the analog-to digital converter and the microprocessor in the Fender patent. The present invention receives the interference pattern between samples of pairs of transmitted laser beams from a CCD camera, then performs a calculation of the difference in optical path lengths between the two beams which allows the laser transmitter to match the phase of the outgoing beams by adjusting the optical path lengths.
The image processor of the present invention returns the optical path differences to the laser transmitter, where it is used to adjust the phase by the correcting mirrors which adjust the optical path lengths of the two outgoing beams. Monochromatic light requires phasing only within a range of one wavelength. Polychromatic sources cannot tolerate 2.pi. ambiguities and therefore require both coarse and fine phase adjustments for multi-wavelength interference. Both the coarse and fine tuning refer to the phase estimating algorithms which provide adjustments to the optical path lengths of the two beams, and form a part of the present invention.
In view of the foregoing discussion, it is apparent that there currently exists the need for an image processor which is capable of estimating the difference in optical path lengths needed to match the phase of two beams of either monochromatic or polychromatic light from the interference pattern of those two beam. The present invention is directed towards satisfying that need.